A mechanically adjustable
reinforced thermoplastic superelastomer
system, with tunable gas-permeability, was developed. The superelastomer
is based on a graft copolymer structure, using commercial butyl rubbers
(or poly(isobutylene-co-isoprene), P(IB-co-I)) and l- or d,l-lactide (LLA or LA)
derived from renewable feedstocks, by a “grafting from”
controlled polymerization. First, hydroxyl-functionalized PIB (PIB-g-(OH)) macroinitiators were prepared through epoxidation
using an economical alternative to m-chloroperoxybenzoic
acid and ring-opening reaction. Second, PIB-based graft copolymers
with end-hydroxylated poly(lactide) as hard side-chains, PIB-g-(P(L)LA–OH)s, were synthesized to target f
P(L)LA of 0.18–0.45, to achieve mechanical
reinforcement and an additional gas barrier. They were subsequently
acetylated with an acetic anhydride to produce PIB-g-(P(L)LA–Ac)s with improved thermal stability. The well-defined
molecular structures indicated controlled P(L)LA lengths, and the
resulting superelastomers demonstrated improved thermal stability
with increased T
d,5%; microphase-separated
structures having spherical and/or elongated features; thermoplastic
behaviors proved by T
ODT, which were much
lower than the resulting T
d,5%; and superior
and adjustable mechanical characterizations, proving to control elastomeric-to-ductile
properties. An oxygen permeability value as low as 27 mL mm m–2 day–1 atm–1 was
achieved by increasing f
P(L)LA to 0.45,
comparable to polyethylene terephthalate. The partially biodegradable
and processable gas barrier films based on these PIB-g-PLLA thermoplastic superelastomers have great potential for the
flexible packaging of food and medical products.
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